Table 1.

Distribution of background characteristics

Background characteristics	Registry cohort n=474 402 N (%)	MoBa n=75 797 N (%)
Maternal age at delivery, years
<25	79 803 (16.8)	8791 (11.6)
25–29	155 866 (32.9)	25 367 (33.5)
30–34	159 001 (33.5)	29 024 (38.3)
35 and older	79 732 (16.8)	12 615 (16.6)
Maternal parity
0	193 503 (40.8)	33 059 (43.6)
1	170 737 (36.0)	27 291 (36.0)
2	78 163 (16.5)	12 009 (15.8)
3+	31 999 (6.8)	3438 (4.5)
Maternal education
Less than high school	NA	6698 (8.8)
High school	NA	23 485 (31.0)
Up to 4 years of college	NA	30 223 (39.9)
>4 years of college	NA	15 018 (19.8)
Missing	NA	373 (0.5)
Maternal prepregnancy body mass index
<18.5	NA	2313 (3.1)
18.5–24.9	NA	47 768 (63.0)
25–29.9	NA	16 391 (21.6)
30 or higher	NA	7122 (9.5)
Missing	NA	2203 (2.9)
Maternal folic acid supplement intake
No	271 981 (57.3)	16 020 (21.1)
Started before pregnancy	76 333 (16.1)	30 835 (40.7)
Started during pregnancy	124 732 (26.3)	28 942 (38.2)
Missing	1356 (0.3)	0 (0)
Maternal smoking during pregnancy
No	317 226 (66.9)	56 564 (74.6)
Only at the beginning of pregnancy (register)/quit by 18 weeks (MoBa)	27 929 (5.9)	10 811 (14.3)
Still smoking end of pregnancy (register)/smoked after 18 weeks (MoBa)	48 855 (10.3)	8057 (10.6)
Missing	80 392 (17.0)	365 (0.5)
Maternal current asthma
No	454 114 (95.7)	73 220 (96.6)
Yes	20 288 (4.3)	2577 (3.4)
Maternal pre-eclampsia
No	456 100 (96.1)	72 914 (96.2)
Yes	18 302 (3.9)	2883 (3.8)
Child gender
Male	243 413 (51.3)	38 811 (51.2)
Female	230 989 (48.7)	36 986 (48.8)
Child preterm birth (<37 gestational weeks)
No	449 218 (94.7)	71 849 (94.8)
Yes	25 184 (5.3)	3646 (4.8)
Missing	0 (0)	302 (0.4)
Child low birth weight (<2500 g)
No	458 572 (96.7)	73 611 (97.1)
Yes	15 830 (3.3)	2146 (2.8)
Missing	0 (0)	40 (0.1)
Child delivered by caesarean section
No	404 328 (85.2)	65 288 (86.1)
Yes	70 074 (14.8)	10 509 (13.9)

MoBa, Norwegian Mother and Child Cohort Study.